全文获取类型
收费全文 | 5392篇 |
免费 | 533篇 |
出版年
2022年 | 33篇 |
2021年 | 92篇 |
2020年 | 50篇 |
2019年 | 67篇 |
2018年 | 67篇 |
2017年 | 53篇 |
2016年 | 103篇 |
2015年 | 203篇 |
2014年 | 210篇 |
2013年 | 298篇 |
2012年 | 309篇 |
2011年 | 334篇 |
2010年 | 197篇 |
2009年 | 197篇 |
2008年 | 266篇 |
2007年 | 292篇 |
2006年 | 273篇 |
2005年 | 259篇 |
2004年 | 220篇 |
2003年 | 257篇 |
2002年 | 219篇 |
2001年 | 111篇 |
2000年 | 102篇 |
1999年 | 108篇 |
1998年 | 80篇 |
1997年 | 59篇 |
1996年 | 48篇 |
1995年 | 57篇 |
1994年 | 38篇 |
1993年 | 33篇 |
1992年 | 67篇 |
1991年 | 65篇 |
1990年 | 65篇 |
1989年 | 72篇 |
1988年 | 54篇 |
1987年 | 66篇 |
1986年 | 46篇 |
1985年 | 48篇 |
1984年 | 58篇 |
1983年 | 65篇 |
1982年 | 45篇 |
1981年 | 33篇 |
1980年 | 35篇 |
1979年 | 45篇 |
1978年 | 30篇 |
1977年 | 38篇 |
1975年 | 28篇 |
1974年 | 30篇 |
1973年 | 29篇 |
1972年 | 41篇 |
排序方式: 共有5925条查询结果,搜索用时 15 毫秒
51.
J. V. Moore Ramona Moses Valerie J. Cowie 《Radiation and environmental biophysics》1985,24(3):211-218
Summary The gross growth rate, histology, cellular kinetics, andin situ radiobiological response have been measured for three murine, keratinising squamous cell carcinomas that differed in their degree of differentiation. Growth rate was fastest in the least-differentiated tumour, slowest in the best-differentiated. However, the kinetics of the compartment of undifferentiated cells that are likely to be radiotherapeutically important, were the same for the three lines. There was no correlation between degree of differentiation and intrinsic or apparent radiosensitivity as measured by the growth delay assay. The radiobiologically best-oxygenated tumour was that which had the largest stromal component and this was not the best-differentiated tumour. 相似文献
52.
M.D. M.P.H. Valerie M. Parisi B.S. Terrance M. Phernetton Ph.D. John H.G. Rankin 《Prostaglandins & other lipid mediators》1985,30(1):125-130
We have previously shown that FPL 55712, a specific leukotriene receptor antagonist, potentiates estrogen induced uterine hyperemia in nonpregnant rabbits. We therefore chose to investigate the vascular responses of pregnant rabbits to leukotriene blockade. Nine unanesthetized animals carrying 46 viable fetuses were used in this study. Regional blood flows were measured by the radioactive microsphere technique. In 5 rabbits control blood flows were measured after vehicle administration and FPL 55712, 1 mg/kg bolus, followed by infusion of 100 ug/kg/min was given via the jugular vein. Regional blood flows were measured again after 10 minutes of infusion. The procedural order was reversed in the remaining 4 animals. Resistance was calculated as mean arterial pressure divided by total flow to an organ. FPL 55712 decreased the blood pressure from 83 ± 2 to 76 ± 3 mmHg (P<.001). Uterine resistance was not significantly changed (387 ± 44 to 362 ± 42 mmHg·ml−1·min·gm), but renal resistance fell from 18.5 ± 1.1 to 15.1 ± 1.2 mmHg·ml−1·min·gm (P<.01). FPL 55712 induced maternal placental vasodilatation with resistance decreasing from 291 ± 33 to 261 ± 31 mmHg·ml−1·min·gm (P<.04). Vehicle administration did not cause dilation in any vascular bed. FPL 55712 appears to be a placental vasodilator whose action is most likely due to receptor blockade of the vasoconstrictive endogenous leukotrienes. 相似文献
53.
Reactions of the UVRABC excision nuclease with DNA damaged by diamminedichloroplatinum(II). 总被引:11,自引:7,他引:4
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mutants of Escherichia coli, which are blocked in excision repair (uvrA6, uvrB5, or uvrC34) are exceptionally sensitive to the antitumor drug cis-Pt(II)(NH3)2Cl2 (cis-DDP) but not the trans isomer. Plasmid DNA, damaged by either the cis or trans compound and treated with the UVRABC excision nuclease was cut as shown by conversion of supercoiled DNA to relaxed forms. All three protein products of the uvrA, uvrB, and uvrC genes were required for incision. End-labeled fragments damaged with cis-DDP and reacted with the UVRABC nuclease were cut at the 8th phosphodiester bond 5' and at the 4th phosphodiester bond 3' to adjacent GG's. DNA treated with trans-DDP was not cut appreciably at adjacent GG's by the repair enzyme as subsequent analysis of reaction products after enzyme digestion gave a pattern similar to those obtained with control untreated fragments. The results indicate that the UVRABC nuclease may promote cell survival by the removal of adjacent GG's which are crosslinked by cis-Pt(II)(NH3)2Cl2. 相似文献
54.
J Beck 《Acta physiologica Polonica》1986,37(4-5):207-212
Bar-press response reinforced by the contact with estrous female were investigated in male rats in two experimental situations, when the visual communication with female was prevented or when it was permitted. After the instrumental responses directly preceded by ejaculations, depending on the increasing duration of response latency, three categories of male behavior were observed: avoiding of the contact with female, precopulatory behavior, or copulatory behavior. The enabling the visual communication with a female caused the significant increase of occurrence of copulatory behavior and significant decrease of contact-avoiding behavior, whereas the precopulatory behavior showed unsignificant increase. It is suggested that when prevented to see the female male rats can perform the instrumental response even when the sexual arousal is to low for precopulatory behavior. Such unrewarded responses lead to the appearance of frustration. On the contrary, when the female is visible the instrumental response is delayed up to the moment when the visual cues coming from female can evoke at least precopulatory behavior. 相似文献
55.
We previously demonstrated inhibition of Na+-dependent 32Pi transport in canine renal brush-border membranes in association with NAD+-induced ADP ribosylation of membrane protein(s) and postulated that NAD+ inhibits Pi transport across the brush-border membrane via ADP ribosylation. Recently it was shown that incubation of rat brush-border membrane with NAD+ resulted in release of Pi which was prevented by EDTA. It was proposed that NAD+-mediated inhibition of 32Pi transport might occur through this mechanism. To determine whether NAD+ inhibited 32Pi transport by a mechanism other than or in addition to release of Pi, we compared Na+-dependent 32Pi counterflow in brush-border membrane equilibrated with Pi or with Pi generated from NAD+. Release of Pi from NAD+ incubated with brush-border membrane was confirmed. The increased uptake of 32Pi which was demonstrated in brush-border membrane equilibrated with Pi was not measured when intravesicular Pi was generated from a concentration of NAD+ which effected ADP-ribosylation of brush border membranes (100 μM NAD+). In contrast, increased uptake of 32Pi was demonstrated when intravesicular Pi was generated from 1 μM NAD+ which did not effect ADP ribosylation. Mg2+-dependent ADP ribosylation of brush-border membrane incubated with NAD+ was demonstrated which persisted during the time interval of 32Pi uptake measurements. Our findings are compatible with the hypothesis that NAD+-induced ADP ribosylation of brush-border membrane protein(s) results in inhibition of Pi transport across the membrane in vivo. EDTA may act to prevent this inhibition in brush-border membrane by chelation of Mg2+ and decreased ADP ribosylation. 相似文献
56.
Uptake of l-[1-14C]ascorbate by intact ascorbate-free spinach (Spinacia oleracea L. cv Vitalr) chloroplasts has been investigated using the technique of silicone oil filtering. Rates greater than 100 micromoles per milligram chlorophyll per hour (external concentration, 10 millimolar) of ascorbate transport were observed. Ascorbate uptake into the sorbitol-impermeable space (stroma) followed the Michaelis-Menten-type characteristic for substrate saturation. A Km of 18 to 40 millimolar was determined. Transport of ascorbate across the chloroplast envelope resulted in an equilibrium of the ascorbate concentrations between stroma and medium. A pH optimum of 7.0 to 7.5 and the lack of alkalization of the medium upon ascorbate uptake suggest that only the monovalent ascorbate anion is able to cross the chloroplast envelope. The activation energy of ascorbate uptake was determined to be 65.8 kilojoules (16 kilocalories) per mole (8 to 20°C). Interference of ascorbate transport with substrates of the phosphate or dicarboxylate translocator could not be detected, but didehydroascorbate was a competitive inhibitor. Preloading of chloroplasts with didehydroascorbate resulted in an increase of Vmax but did not change the Km for ascorbate. Millimolar concentrations of the sulfhydryl reagent p-chloromercuriphenyl sulfonate inhibited ascorbate uptake. The data are interpreted in terms of ascorbate uptake into chloroplasts by the mechanism of facilitated diffusion mediated by a specific translocator. 相似文献
57.
A new simple and sensitive in-vitro method for the diagnosis of type 1 (IgE-mediated) hypersensitivity in man is described. Sliced human skin is passively sensitized by reaginic serum from allergic patients and the presence of antigen-specific IgE on the sensitized slices is detected by assay of antigen-evoked histamine release. Serum from 12 out of 14 patients with clinical respiratory allergy and positive skin tests gave significant antigen-specific histamine release. This method, which is essentially an in-vitro model of the Prausnitz-Küstner reaction, should prove of value in the diagnosis of human reaginic hypersensitivity in man. 相似文献
58.
59.
60.